CN103605085A - LED thermal characteristic test method based on structure function - Google Patents

Abstract

The invention relates to a LED light source construction body and discloses a LED thermal characteristic test method based on a structure function. The method comprises the following steps that two groups of LED lamps with different packaging structures are selected, wherein packaging bodies and materials of the two groups of LED lamps are different; through using a characteristic of a linear relation which is formed by a LED U-I curve drifting under a small current situation and a PN joint temperature, a node voltage VF and a temperature TJ of the lamps driven by a constant current are recorded and a proportion coefficient S is calculated; when a transient cooling curve is measured, the two groups of LED lamps are placed at a 25-27 DEG C ambient temperature, a 350mA rated current is used to drive a sample for 10mins so that a heat stable state is reached, and then it begins to record a cooling curve during a transient test; a piece of paper is placed below the sample so that isolation performance is achieved, then different heat dissipation plates are used to record an obtained curve; according to the cooling curve, software is used to analyze and calculate a differential structure function Rth, and the structure of the tested LED lamps and an inflection point position in the curve are combined so that a thermal resistance K from a LED chip to a pin is obtained.

Description

A kind of LED thermal characteristics method of testing based on structure function

Technical field

The present invention relates to LED light source tectosome, exactly, is a kind of LED thermal characteristics method of testing based on structure function.

Background technology

LED be called as the 4th generation lighting source, the advantages such as light efficiency is high, energy-conserving and environment-protective, the life-span is long, volume is little that it has, are widely used in the fields such as pilot lamp, signal lamp, Landscape Lighting.But along with the increase of LED power input, can cause chip temperature to raise, thereby affect the parameters such as luminous flux, color and predominant wavelength of LED, LED ageing process is accelerated, lose efficacy in advance.Especially for high power LED device, thermal characteristic can have influence on its working temperature, life-span and luminescence efficiency.Therefore, heat radiation is that great power LED enters one of important bottleneck of general illumination, and the measurement of the thermal characteristic parameters such as the junction temperature of great power LED, thermal resistance is become to most important.

At present, LED thermal characteristic measurement method is a lot, and as forward voltage method is measured LED junction temperature, the difficult point of the method is to measure the temperature of LED base, thereby can cause measuring result error bigger than normal.In addition, also have infrared imaging method, electrical parameter method etc.But more or less all there are some defects in these methods.As slow in infrared imaging method speed, be subject to spatial resolution limitations; Electrical parameter method has been ignored the test to device loss luminous power, when test great power LED, can produce relatively large deviation.

Technological deficiency in view of above-mentioned LED thermal characteristics method of testing, the present invention adopts thermal transient analysis of test methods LED device to be measured thermal characteristic, the i.e. test of the thermal characteristics based on structure function, this method of testing to LED without destructiveness, reduced the error that causes measurement result to produce owing to affecting LED inner structure, meanwhile, this measuring method mainly depends on the software analysis of hot tester, result is clear, is convenient to researcher the thermal behavior of LED is analyzed.

Summary of the invention

Technical matters to be solved by this invention is by thermal transient analysis of test methods LED device to be measured thermal characteristic, the i.e. test of the thermal characteristics based on structure function, this method of testing to LED without destructiveness, reduced the error that causes measurement result to produce owing to affecting LED inner structure, rely on the software analysis of hot tester simultaneously, a kind of LED thermal characteristics method of testing based on structure function is provided.

The technical scheme that the present invention solves the problems of the technologies described above is as follows: a kind of LED thermal characteristics method of testing based on structure function, and described method comprises as follows:

(1) select the LED light fixture of two groups of different encapsulating structures, the packaging body of described two groups of LED light fixtures is different from material;

(2) feature of the linear relationship that U-I curves shift of utilizing LED forms with PN junction temperature under little current conditions, records the node voltage V under constant current drives of two groups of light fixtures _fwith temperature T _j, calculate respectively their scale-up factor S;

$S=\frac{{\mathrm{dV}}_F}{{\mathrm{dT}}_J}$

(3) while measuring transient state temperature lowering curve, respectively two groups of LED light fixtures are placed under the environment temperature of 25～75 ℃, with the rated current driving sample 10min of 350mA, reach after hot stable state, transient test starts to record temperature lowering curve;

(4) by put a piece of paper below sample, do and isolate, then adopt different heat sinks, record curve obtained and contrast with temperature lowering curve;

(5) according to temperature lowering curve, utilize software analysis computing differential structure function R _th, in conjunction with the structure of tested LED light fixture and the corner position in curve, obtain LED chip to the thermal resistance K of pin.

The invention has the beneficial effects as follows: from the volt-ampere-temperature characteristics of LED, calculate S coefficient, according to S coefficient and temperature lowering curve, pass through software analysis chip to the thermal resistance of LED pin.Adopt indirect means for this method to measure the Photothermal characterisation In of LED light fixture, there is the test duration short, operate relatively simple, thereby reduce the packaging thermal resistance of LED, improve the package quality of LED, and then the serviceable life of prolongation LED.

Accompanying drawing explanation

Fig. 1 is flow chart of steps of the present invention.

Embodiment

Below in conjunction with accompanying drawing, principle of the present invention and feature are described, example, only for explaining the present invention, is not intended to limit scope of the present invention.

As shown in Figure 1, a kind of LED thermal characteristics method of testing based on structure function, described method comprises as follows:

(1) select the LED light fixture of two groups of different encapsulating structures, the packaging body of described two groups of LED light fixtures is different from material; For example, first group is white light LEDs, and its encapsulating structure is simple, is followed successively by from inside to outside chip, packaging body, is imitative lumen structure; Second group is yellow light LED, and its encapsulating structure and first group of sample are similar, but packaging body is different with first group from material.

(2) feature of the linear relationship that U-I curves shift of utilizing LED forms with PN junction temperature under little current conditions, due to the heating curves of LED refer to electric current by little current switching to large electric current, measuring error is larger; Otherwise temperature lowering curve, the electric current that flows through LED is very little, and measuring accuracy is higher; Heating curves and cooling curve are symmetrical again.Record the node voltage V under constant current drives of two groups of light fixtures _fwith temperature T _j, calculate respectively their scale-up factor S.

$S=\frac{{\mathrm{dV}}_F}{{\mathrm{dT}}_J}$

(3) while measuring transient state temperature lowering curve, respectively two groups of LED light fixtures are placed under the environment temperature of 25～75 ℃, with the rated current driving sample 10min of 350mA, reach after hot stable state, transient test starts to record temperature lowering curve;

(4) by put a piece of paper below sample, do and isolate, then adopt different heat sinks, record curve obtained and contrast with temperature lowering curve;

(5) according to temperature lowering curve, utilize software analysis computing differential structure function R _th, in conjunction with the structure of tested LED light fixture and the corner position in curve, obtain LED chip to the thermal resistance K of pin.

The LED structure of two kinds of samples is different, color is different, S coefficient and the thermal resistance that obtains of structure function figure by them distribute also different, in actual production, just can the structure of LED be optimized with reference to these thermal characteristic parameters, thus the packaging thermal resistance of reduction LED, improve the package quality of LED, and then increase the service life.

The foregoing is only preferred embodiment of the present invention, in order to limit the present invention, within the spirit and principles in the present invention not all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (1)

1. the LED thermal characteristics method of testing based on structure function, is characterized in that, described method comprises as follows:

(1) select the LED light fixture of two groups of different encapsulating structures, the packaging body of described two groups of LED light fixtures is different from material;

(2) feature of the linear relationship that U-I curves shift of utilizing LED forms with PN junction temperature under little current conditions, records the node voltage V under constant current drives of two groups of light fixtures _fwith temperature T _j, calculate respectively their scale-up factor S;

$S=\frac{{\mathrm{dV}}_F}{{\mathrm{dT}}_J}$

(3) while measuring transient state temperature lowering curve, respectively two groups of LED light fixtures are placed under the environment temperature of 25～75 ℃, with the rated current driving sample 10min of 350mA, reach after hot stable state, transient test starts to record temperature lowering curve;

(4) by put a piece of paper below sample, do and isolate, then adopt different heat sinks, record curve obtained and contrast with temperature lowering curve;

(5) according to temperature lowering curve, utilize software analysis computing differential structure function R _th, in conjunction with the structure of tested LED light fixture and the corner position in curve, obtain LED chip to the thermal resistance K of pin.